The present invention generally relates to electricity meters, and more particularly, to self-calibrating electricity meters suitable for use in polyphase power configurations.
Electrical utility service providers, or simply utilities, generate polyphase electrical power, and typically three phase power. Polyphase electrical power is alternating current (xe2x80x9cACxe2x80x9d) electrical power that is supplied on a plurality of power supply lines wherein the voltage waveform on each of the power supply lines has a unique phase angle. While only a single phase of the polyphase electrical power may typically be provided for single family residences, true polyphase electrical power is typically provided to larger facilities such as commercial and industrial facilities.
Utilities monitor energy usage by customers through electricity meters. Electricity meters track among other things, the amount of energy consumed, typically measured in kilowatt-hours (xe2x80x9ckwhxe2x80x9d), at each customer""s facility. The utility uses the consumption information primarily for billing, but also for resource allocation planning and other purposes.
Utilities are frequently required by state or local regulations or by energy customers to verify the accuracy of electricity meters operating in the field. To satisfy these requirements, utilities typically test the accuracy of each meter upon receipt from a manufacturer. Should the results of such testing indicate that a given meter is not operating at a desired degree of accuracy, the meter is adjusted so as to improve its accuracy. This process of testing and adjusting is often referred to as calibration.
In general, calibration typically involves comparing a power reading obtained using a meter under test against that measured by a standard meter, and adjusting the former as appropriate. Conventionally, the process of calibrating an electricity meter has required a separate computing device to calculate calibration data (e.g., coefficients) which are used to adjust the meter. Accordingly, there is a need for an electricity meter that is capable of internally calculating calibration data, thereby performing a calibration operation without the need for a separate computing device. That is, it is desirable for a meter to perform xe2x80x9cself-calibration.xe2x80x9d Moreover, it is also desirable to provide a configuration where a plurality of such self-calibrating meters can be calibrated at the same time. The present invention addresses these and other problems.
According to the present invention, a self-calibrating electricity meter includes a measurement circuit for generating power information representative of measured power. A controller is operably coupled to the measurement circuit and includes an input for receiving reference standard information. The controller compares the power information generated by the measurement circuit to the reference standard information and generates a compensation signal in dependence upon the comparison. The compensation signal is used to calibrate the measurement circuit. Preferably, the meter is capable of being electrically connected to, and calibrated concurrently with at least one other meter.
According to an aspect of the invention, the measurement circuit multiplies current measurement signals by a scalar quantity in dependence upon the compensation signal. According to another aspect of the invention, the measurement circuit imposes a time delay upon current measurement signals in dependence upon the compensation signal.
According to a preferred embodiment, the self-calibrating meter includes a display for providing a visual indication of a calibration state of the meter. According to an aspect of the invention, the display illuminates a green light to indicate that the meter has been successfully calibrated. According to another aspect of the invention, the display illuminates a red light to indicate that the meter has been unsuccessfully calibrated. According to yet another aspect of the invention, the display illuminates a yellow light to indicate that calibration is in progress.
According to a preferred embodiment, the calibration is performed in a plurality of intervals, wherein a first interval is used to calibrate current magnitude measurements, a second interval is used to calibrate current phase angle measurements, and a third interval is used to verify calibration of the current magnitude measurements and the current phase angle measurements.